1. Field of the Invention
This invention relates to a color separation optical system for a color television camera, and more particularly to an improvement in a color separation optical system for a color television camera of the relay lens type.
2. Description of the Prior Art
A color separation optical system for a color television camera of the so called relay lens type includes a relay lens system between the taking lens and the image pickup tubes of the camera. The relay lens system divides an image of the object of the camera focused by the taking lens into three color images of red, green and blue. The three color images are then focused on the three image pick-up tubes. The relay lens system comprises a single first relay lens, color separation optical elements such as prism blocks or dichroic mirrors, and three second relay lenses, one for each of the three color images. In the color separation optical system of the relay lens type as described above, two color images are obtained by reflection and one color image is obtained by transmission from the color separation optical elements, and it is possible to make the optical axes of the two second relay lenses for the two color images obtained by reflection parallel to the optical axis of the other second relay lens for the other color image obtained by transmission. Therefore, it is possible to orient the three color tubes in parallel to each other and accordingly to make the size of the television camera compact and avoid the influence of terrestrial magnetism on the tubes.
The image pick-up tubes employed in the color television camera in combination with the color separation optical system are incorporated in coil assemblies so that the focus control and the deflection and scanning of the electron beams thereof may be conducted thereby. In combining the pick-up tubes with the color separation optical system, it is necessary to precisely locate the tubes mounted in the coil assembly with respect to the focal planes of the color separation optical system. Further, it is also necessary to adjust the angular position of the pick-up tubes with respect to the color separation optical system by rotating the tubes together with the coil assemblies in order to obtain a precise registration between the three color images formed on the three tubes.
In order to make the above described control or adjustment, the coil assemblies including the image pick-up tubes are each supported by a coil assembly support means provided with a focusing means and a rotating means.
The above described coil assembly for the image pick-up tubes suffers from certain defects. Since it is very difficult to precisely adjust the position of the coil assembly because of the error in its outer diameter and since it has a comparatively large weight, the coil assembly support means is inevitably complicated in its structure and is large and expensive. Further, a coil assembly is necessary for each of the three color image pick-up tubes. Therefore, the coil assemblies provided with focusing means as well as rotating means are inevitably separated from each other by a distance larger than that optically required. In other words, the optical axes of the three tubes are separated from each other by a distance greater than that required for purely optical reasons. Consequently, the overall size of the color separation optical system becomes large.